[time-nuts] 1 pps correction

[Chris Albertson]

The simplest way to do this is to use a "standard" GPS and let if
drive a GPSDO.  Yes you can try and build a copy of a T-bolt but how
many engineering ours do you think Trimble spent on that?  Well over a
man year I'd say and few people have the range of skills needed to do
it all themselves.

If you want to use the sawtooth data in the GPSDO then you'd need a
one of those very small 8-pin micro controllers.  It could "tap" the
serial line and listen for the sawtooth correction and then output a
voltage on an analog pin.   The sawtooth correction does not change
very fast so the bandwidth is low enough for something like an AVR or
PIC.  This uP would have only one function so the software would be
easy
I think you'd use the analog sawtooth voltage to slightly bias the
phase detector.



On Sat, Apr 7, 2012 at 3:59 AM, Attila Kinali <attila at kinali.ch> wrote:
> On Sun, 1 Apr 2012 19:10:59 +0000
> shalimr9 at gmail.com wrote:
>
>> It seems to me that if standalone GPS timing receivers used a VCXO
>> instead of a fixed frequency clock, the cost delta would not be that
>> significant, and they too could avoid the need for sawtooth correction.
>
> Not really. You'd need a low noise, low DNL, high resolution DAC to
> stear the VCXO. Analog electronic costs considerably more than a tiny bit
> of software and eats a lot more power.
>
> Maybe you can get away with using one of the Silicon Labs programmable
> oscillators instead of a VCXO and a DAC. But IIRC they only have a
> frequency setting, no phase setting, so you need some way to fix the
> phase offset.
>
>                        Attila Kinali
>
>
> --
> Why does it take years to find the answers to
> the questions one should have asked long ago?
>
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-- 

Chris Albertson
Redondo Beach, California